Conveying a Certificate Signing Request (CSR) in a Secure Zero Touch Provisioning (SZTP) Bootstrapping Request
draft-ietf-netconf-sztp-csr-05
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Active".
|
|
|---|---|---|---|
| Authors | Kent Watsen , Russ Housley , Sean Turner | ||
| Last updated | 2021-07-07 | ||
| Replaces | draft-kwatsen-netconf-sztp-csr | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews |
YANGDOCTORS Last Call review
(of
-02)
by Joe Clarke
Ready w/nits
|
||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | Mahesh Jethanandani | ||
| Shepherd write-up | Show Last changed 2021-06-02 | ||
| IESG | IESG state | AD Evaluation::AD Followup | |
| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | Robert Wilton | ||
| Send notices to | mjethanandani@gmail.com |
draft-ietf-netconf-sztp-csr-05
NETCONF Working Group K. Watsen
Internet-Draft Watsen Networks
Updates: 8572 (if approved) R. Housley
Intended status: Standards Track Vigil Security, LLC
Expires: 8 January 2022 S. Turner
sn3rd
7 July 2021
Conveying a Certificate Signing Request (CSR) in a Secure Zero Touch
Provisioning (SZTP) Bootstrapping Request
draft-ietf-netconf-sztp-csr-05
Abstract
This draft extends the "get-bootstrapping-data" RPC defined in RFC
8572 to include an optional certificate signing request (CSR),
enabling a bootstrapping device to additionally obtain an identity
certificate (e.g., an LDevID, from IEEE 802.1AR) as part of the
"onboarding information" response provided in the RPC-reply.
Editorial Note (To be removed by RFC Editor)
This draft contains many placeholder values that need to be replaced
with finalized values at the time of publication. This note
summarizes all of the substitutions that are needed. No other RFC
Editor instructions are specified elsewhere in this document.
Artwork in this document contains shorthand references to drafts in
progress. Please apply the following replacements:
* "XXXX" --> the assigned numerical RFC value for this draft
* "AAAA" --> the assigned RFC value for I-D.ietf-netconf-crypto-
types
Artwork in this document contains a placeholder value for the
publication date of this draft. Please apply the following
replacement:
* "2021-07-07" --> the publication date of this draft
This document contains references to other drafts in progress, both
in the Normative References section, as well as in body text
throughout. Please update the following references to reflect their
final RFC assignments:
* I-D.ietf-netconf-crypto-types
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* I-D.ietf-netconf-keystore
* I-D.ietf-netconf-trust-anchors
* I-D.ietf-netmod-factory-default
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 8 January 2022.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
1.3. Requirements Language . . . . . . . . . . . . . . . . . . 4
1.4. Conventions . . . . . . . . . . . . . . . . . . . . . . . 4
2. The "ietf-sztp-csr" Module . . . . . . . . . . . . . . . . . 4
2.1. Data Model Overview . . . . . . . . . . . . . . . . . . . 4
2.2. Example Usage . . . . . . . . . . . . . . . . . . . . . . 7
2.3. YANG Module . . . . . . . . . . . . . . . . . . . . . . . 13
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3. Security Considerations . . . . . . . . . . . . . . . . . . . 23
3.1. SZTP-Client Considerations . . . . . . . . . . . . . . . 23
3.1.1. Ensuring the Integrity of Asymmetric Private Keys . . 23
3.1.2. Reuse of a Manufacturer-generated Private Key . . . . 23
3.1.3. Replay Attack Protection . . . . . . . . . . . . . . 24
3.1.4. Connecting to an Untrusted Bootstrap Server . . . . . 24
3.1.5. Selecting the Best Origin Authentication Mechanism . 25
3.1.6. Clearing the Private Key and Associated
Certificate . . . . . . . . . . . . . . . . . . . . . 25
3.2. SZTP-Server Considerations . . . . . . . . . . . . . . . 25
3.2.1. Conveying Proof of Possession to a CA . . . . . . . . 25
3.2.2. Supporting SZTP-Clients that don't trust the
SZTP-Server . . . . . . . . . . . . . . . . . . . . . 26
3.2.3. YANG Module Considerations . . . . . . . . . . . . . 26
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
4.1. The "IETF XML" Registry . . . . . . . . . . . . . . . . . 26
4.2. The "YANG Module Names" Registry . . . . . . . . . . . . 27
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.1. Normative References . . . . . . . . . . . . . . . . . . 27
5.2. Informative References . . . . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29
1. Introduction
1.1. Overview
This draft extends the "get-bootstrapping-data" RPC defined in
[RFC8572] to include an optional certificate signing request (CSR)
[RFC2986], enabling a bootstrapping device to additionally obtain an
identity certificate (e.g., an LDevID [Std-802.1AR-2018]) as part of
the "onboarding information" response provided in the RPC-reply.
The ability to provision an identity certificate that is purpose-
built for a production environment during the bootstrapping process
removes reliance on the manufacturer CA, and it also enables the
bootstraped device to join the production environment with an
appropriate identity and other attributes in its LDevID certificate.
1.2. Terminology
This document uses the following terms from [RFC8572]:
* Bootstrap Server
* Bootstrapping Data
* Conveyed Information
* Device
* Manufacturer
* Onboarding Information
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* Signed Data
This document defines the following new terms:
SZTP-client The term "SZTP-client" refers to a "device" that is
using a "bootstrap server" as a source of "bootstrapping data".
SZTP-server The term "SZTP-server" is an alternative term for
"bootstrap server" that is symmetric with the "SZTP-client" term.
1.3. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
1.4. Conventions
Various examples used in this document use a placeholder value for
binary data that has been base64 encoded (e.g., "BASE64VALUE=").
This placeholder value is used as real base64 encoded structures are
often many lines long and hence distracting to the example being
presented.
2. The "ietf-sztp-csr" Module
This section defines a YANG 1.1 [RFC7950] module that augments the
"ietf-sztp-bootstrap-server" module defined in [RFC8572] and defines
a YANG "structure".
The augmentation adds two nodes ("csr-support" and "csr") to the
"input" parameter of the "get-bootstrapping-data" RPC defined in
[RFC8572].
The YANG structure, "request-info", defines data returned in the
"error-info" node defined in Section 7.1 of [RFC8040].
2.1. Data Model Overview
The following tree diagram [RFC8340] illustrates the "ietf-sztp-csr"
module. The diagram shows the definition of an augmentation adding
descendant nodes "csr-support" and "csr" and the definition of a
structure called "request-info".
In the order of their intended use:
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* The "csr-support" node is used by the SZTP-client to signal to the
SZTP-server that it supports the ability the generate CSRs, per
this specification. The "csr-support" parameter carries details
regarding the SZTP-client's ability to generate CSRs.
* The "request-info" structure is used by the SZTP-server to signal
back to the SZTP-client its desire to sign a CSR. The "request-
info" structure additionally communicates details about the CSR
the SZTP-client is to generate.
* The "csr" node is used by the SZTP-client to communicate its CSR
to the SZTP-server. Not shown is how the SZTP-server communicates
the signed certificate to the SZTP-client; how to do this is
discussed later in this document.
module: ietf-sztp-csr
augment /sztp-svr:get-bootstrapping-data/sztp-svr:input:
+---w (msg-type)?
+--:(csr-support)
| +---w csr-support!
| +---w key-generation!
| | +---w supported-algorithms
| | +---w algorithm-identifier* binary
| +---w csr-generation
| +---w supported-formats
| +---w format-identifier* identityref
+--:(csr)
+---w csr!
+---w (request-type)
+--:(p10)
| +---w p10? ct:csr
+--:(cmc)
| +---w cmc? binary
+--:(cmp)
+---w cmp? binary
structure: request-info
+--ro key-generation!
| +--ro selected-algorithm
| +--ro algorithm-identifier binary
+--ro csr-generation
| +--ro selected-format
| +--ro format-identifier identityref
+--ro cert-req-info? ietf-crypto-types:csr-info
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To further illustrate how the augmentation and structure defined by
the "ietf-sztp-csr" module are used, below are two additional tree
diagrams showing these nodes placed where they are used.
The following tree diagram [RFC8340] illustrates SZTP's "get-
bootstrapping-data" RPC with the augmentation in place.
=============== NOTE: '\' line wrapping per RFC 8792 ================
module: ietf-sztp-bootstrap-server
rpcs:
+---x get-bootstrapping-data
+---w input
| +---w signed-data-preferred? empty
| +---w hw-model? string
| +---w os-name? string
| +---w os-version? string
| +---w nonce? binary
| +---w (sztp-csr:msg-type)?
| +--:(sztp-csr:csr-support)
| | +---w sztp-csr:csr-support!
| | +---w sztp-csr:key-generation!
| | | +---w sztp-csr:supported-algorithms
| | | +---w sztp-csr:algorithm-identifier* bina\
ry
| | +---w sztp-csr:csr-generation
| | +---w sztp-csr:supported-formats
| | +---w sztp-csr:format-identifier* identit\
yref
| +--:(sztp-csr:csr)
| +---w sztp-csr:csr!
| +---w (sztp-csr:request-type)
| +--:(sztp-csr:p10)
| | +---w sztp-csr:p10? ct:csr
| +--:(sztp-csr:cmc)
| | +---w sztp-csr:cmc? binary
| +--:(sztp-csr:cmp)
| +---w sztp-csr:cmp? binary
+--ro output
+--ro reporting-level? enumeration {onboarding-server}?
+--ro conveyed-information cms
+--ro owner-certificate? cms
+--ro ownership-voucher? cms
The following tree diagram [RFC8340] illustrates RESTCONF's "errors"
RPC-reply message with the "request-info" structure in place.
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module: ietf-restconf
+--ro errors
+--ro error* []
+--ro error-type enumeration
+--ro error-tag string
+--ro error-app-tag? string
+--ro error-path? instance-identifier
+--ro error-message? string
+--ro error-info
+--ro request-info
+--ro key-generation!
| +--ro selected-algorithm
| +--ro algorithm-identifier binary
+--ro csr-generation
| +--ro selected-format
| +--ro format-identifier identityref
+--ro cert-req-info? ct:csr-info
2.2. Example Usage
| The examples below are encoded using JSON, but they could
| equally well be encoded using XML, as is supported by SZTP.
An SZTP-client implementing this specification would signal to the
bootstrap server its willingness to generate a CSR by including the
"csr-support" node in its "get-bootstrapping-data" RPC, as
illustrated below.
REQUEST
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=============== NOTE: '\' line wrapping per RFC 8792 ================
POST /restconf/operations/ietf-sztp-bootstrap-server:get-bootstrappi\
ng-data HTTP/1.1
HOST: example.com
Content-Type: application/yang.data+json
{
"ietf-sztp-bootstrap-server:input" : {
"hw-model": "model-x",
"os-name": "vendor-os",
"os-version": "17.3R2.1",
"nonce": "extralongbase64encodedvalue=",
"ietf-sztp-csr:csr-support": {
"key-generation": {
"supported-algorithms": {
"algorithm-identifier": [
"BASE64VALUE1",
"BASE64VALUE2",
"BASE64VALUE3"
]
}
},
"csr-generation": {
"supported-formats": {
"format-identifier": [
"ietf-sztp-csr:p10",
"ietf-sztp-csr:cmc",
"ietf-sztp-csr:cmp"
]
}
}
}
}
}
Assuming the SZTP-server wishes to prompt the SZTP-client to provide
a CSR, then it would respond with an HTTP 400 Bad Request error code:
RESPONSE
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HTTP/1.1 400 Bad Request
Date: Sat, 31 Oct 2015 17:02:40 GMT
Server: example-server
Content-Type: application/yang.data+json
{
"ietf-restconf:errors" : {
"error" : [
{
"error-type": "application",
"error-tag": "missing-attribute",
"error-message": "Missing input parameter",
"error-info": {
"ietf-sztp-csr:request-info": {
"key-generation": {
"selected-algorithm": {
"algorithm-identifier": "BASE64VALUE="
}
},
"csr-generation": {
"selected-format": {
"format-identifier": "ietf-sztp-csr:cmc"
}
},
"cert-req-info": "BASE64VALUE="
}
}
}
]
}
}
Upon being prompted to provide a CSR, the SZTP-client would POST
another "get-bootstrapping-data" request, but this time including the
"csr" node to convey its CSR to the SZTP-server:
REQUEST
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=============== NOTE: '\' line wrapping per RFC 8792 ================
POST /restconf/operations/ietf-sztp-bootstrap-server:get-bootstrappi\
ng-data HTTP/1.1
HOST: example.com
Content-Type: application/yang.data+json
{
"ietf-sztp-bootstrap-server:input" : {
"hw-model": "model-x",
"os-name": "vendor-os",
"os-version": "17.3R2.1",
"nonce": "extralongbase64encodedvalue=",
"ietf-sztp-csr:csr": {
"p10": "BASE64VALUE="
}
}
}
The SZTP-server responds with "onboarding-information" (encoded
inside the "conveyed-information" node) containing a signed identity
certificate for the CSR provided by the SZTP-client:
RESPONSE
HTTP/1.1 200 OK
Date: Sat, 31 Oct 2015 17:02:40 GMT
Server: example-server
Content-Type: application/yang.data+json
{
"ietf-sztp-bootstrap-server:output" : {
"reporting-level": "verbose",
"conveyed-information": "BASE64VALUE="
}
}
How the signed certificate is conveyed inside the onboarding
information is outside the scope of this document. Some
implementations may choose to convey it inside a script (e.g., SZTP's
"pre-configuration-script"), while other implementations may choose
to convey it inside the SZTP "configuration" node. SZTP onboarding
information is described in Section 2.2 of [RFC8572].
Following are two examples of conveying the signed certificate inside
the "configuration" node. Both examples assume that the SZTP-client
understands the "ietf-keystore" module defined in
[I-D.ietf-netconf-keystore].
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This first example illustrates the case where the signed certificate
is for the same asymmetric key used by the SZTP-client's
manufacturer-generated identity certificate (e.g., an IDevID, from
[Std-802.1AR-2018]). As such, the configuration needs to associate
the newly signed certificate with the existing asymmetric key:
=============== NOTE: '\' line wrapping per RFC 8792 ================
{
"ietf-keystore:keystore": {
"asymmetric-keys": {
"asymmetric-key": [
{
"name": "Manufacturer-Generated Hidden Key",
"public-key-format": "ietf-crypto-types:subject-public-key\
-info-format",
"public-key": "BASE64VALUE=",
"hidden-private-key": [null],
"certificates": {
"certificate": [
{
"name": "Manufacturer-Generated IDevID Cert",
"cert-data": "BASE64VALUE="
},
{
"name": "Newly-Generated LDevID Cert",
"cert-data": "BASE64VALUE="
}
]
}
}
]
}
}
}
This second example illustrates the case where the signed certificate
is for a newly generated asymmetric key. As such, the configuration
needs to associate the newly signed certificate with the newly
generated asymmetric key:
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=============== NOTE: '\' line wrapping per RFC 8792 ================
{
"ietf-keystore:keystore": {
"asymmetric-keys": {
"asymmetric-key": [
{
"name": "Manufacturer-Generated Hidden Key",
"public-key-format": "ietf-crypto-types:subject-public-key\
-info-format",
"public-key": "BASE64VALUE=",
"hidden-private-key": [null],
"certificates": {
"certificate": [
{
"name": "Manufacturer-Generated IDevID Cert",
"cert-data": "BASE64VALUE="
}
]
}
},
{
"name": "Newly-Generated Hidden Key",
"public-key-format": "ietf-crypto-types:subject-public-key\
-info-format",
"public-key": "BASE64VALUE=",
"hidden-private-key": [null],
"certificates": {
"certificate": [
{
"name": "Newly-Generated LDevID Cert",
"cert-data": "BASE64VALUE="
}
]
}
}
]
}
}
}
In addition to configuring the signed certificate, it is often
necessary to also configure the Issuer's signing certificate so that
the device (i.e., STZP-client) can authenticate certificates
presented by peer devices signed by the same issuer as its own.
While outside the scope of this document, one way to do this would be
to use the "ietf-truststore" module defined in
[I-D.ietf-netconf-trust-anchors].
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2.3. YANG Module
This module augments an RPC defined in [RFC8572], uses a data type
defined in [I-D.ietf-netconf-crypto-types], has normative references
to [RFC2986] and [ITU.X690.2015], and an informative reference to
[Std-802.1AR-2018].
<CODE BEGINS> file "ietf-sztp-csr@2021-07-07.yang"
module ietf-sztp-csr {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-sztp-csr";
prefix sztp-csr;
import ietf-sztp-bootstrap-server {
prefix sztp-svr;
reference
"RFC 8572: Secure Zero Touch Provisioning (SZTP)";
}
import ietf-yang-structure-ext {
prefix sx;
reference
"RFC 8791: YANG Data Structure Extensions";
}
import ietf-crypto-types {
prefix ct;
reference
"RFC AAAA: YANG Data Types and Groupings for Cryptography";
}
organization
"IETF NETCONF (Network Configuration) Working Group";
contact
"WG Web: http://tools.ietf.org/wg/netconf
WG List: <mailto:netconf@ietf.org>
Authors: Kent Watsen <mailto:kent+ietf@watsen.net>
Russ Housley <mailto:housley@vigilsec.com>
Sean Turner <mailto:sean@sn3rd.com>";
description
"This module augments the 'get-bootstrapping-data' RPC,
defined in the 'ietf-sztp-bootstrap-server' module from
SZTP (RFC 8572), enabling the SZTP-client to obtain a
signed identity certificate (e.g., an LDevID from IEEE
802.1AR) as part of the SZTP onboarding information
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response.
Copyright (c) 2020 IETF Trust and the persons identified
as authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with
or without modification, is permitted pursuant to, and
subject to the license terms contained in, the Simplified
BSD License set forth in Section 4.c of the IETF Trust's
Legal Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC XXXX
(https://www.rfc-editor.org/info/rfcXXXX); see the RFC
itself for full legal notices.
The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',
'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this
document are to be interpreted as described in BCP 14
(RFC 2119) (RFC 8174) when, and only when, they appear
in all capitals, as shown here.";
revision 2021-07-07 {
description
"Initial version";
reference
"RFC XXXX: Conveying a Certificate Signing Request (CSR)
in a Secure Zero Touch Provisioning (SZTP)
Bootstrapping Request";
}
identity certificate-request-format {
description
"A base identity for the request formats supported
by the SZTP-client.
Additional derived identities MAY be defined by
future efforts.";
}
identity p10 {
base certificate-request-format;
description
"Indicates that the SZTP-client supports generating
requests using the 'CertificationRequest' structure
defined in RFC 2986.";
reference
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"RFC 2986: PKCS #10: Certification Request Syntax
Specification Version 1.7";
}
identity cmc {
base certificate-request-format;
description
"Indicates that the SZTP-client supports generating
requests using a constrained version of the 'Full
PKI Request' structure defined in RFC 5272.";
reference
"RFC 5272: Certificate Management over CMS (CMC)";
}
identity cmp {
base certificate-request-format;
description
"Indicates that the SZTP-client supports generating
requests that contain a PKCS#10 Certificate Signing
Request (p10cr), as defined in RFC 2986, encapsulated
in a Nested Message Content (nested), as defined in
RFC 4210.";
reference
"RFC 2986: PKCS #10: Certification Request Syntax
Specification Version 1.7
RFC 4210: Internet X.509 Public Key Infrastructure
Certificate Management Protocol (CMP)";
}
// Protocol-accessible nodes
augment "/sztp-svr:get-bootstrapping-data/sztp-svr:input" {
description
"This augmentation adds the 'csr-support' and 'csr' nodes to
the SZTP (RFC 8572) 'get-bootstrapping-data' request message,
enabling the SZTP-client to obtain an identity certificate
(e.g., an LDevID from IEEE 802.1AR) as part of the onboarding
information response provided by the SZTP-server.
The 'csr-support' node enables the SZTP-client to indicate
that it supports generating certificate signing requests
(CSRs), and to provide details around the CSRs it is able
to generate.
The 'csr' node enables the SZTP-client to relay a CSR to
the SZTP-server.";
reference
"IEEE 802.1AR: IEEE Standard for Local and metropolitan
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area networks - Secure Device Identity
RFC 8572: Secure Zero Touch Provisioning (SZTP)";
choice msg-type {
description
"Only a 'csr-support' or a 'csr' message may be sent.";
container csr-support {
presence
"Indicates that the SZTP-client is capable of sending
CSRs.";
description
"The 'csr-support' node enables the SZTP-client to
indicate that it supports generating certificate
signing requests (CSRs), and provide details around
the CSRs it is able to generate.
When present, the SZTP-server MAY respond with the HTTP
code 400 Bad Request with an 'ietf-restconf:errors'
document having the 'error-tag' value 'missing-attribute'
and the 'error-info' node containing the 'request-info'
structure described in this module.";
container key-generation {
presence
"Indicates that the SZTP-client is capable of
generating a new asymmetric key pair.
If this node is not present, the SZTP-server MAY
request a CSR using the asymmetric key associated
with the device's existing identity certificate
(e.g., an IDevID from IEEE 802.1AR).";
description
"Specifies details for the SZTP-client's ability to
generate a new asymmetric key pair.";
container supported-algorithms {
description
"A list of public key algorithms supported by the
SZTP-client for generating a new key.";
leaf-list algorithm-identifier {
type binary;
min-elements 1;
description
"An AlgorithmIdentifier, as defined in RFC 2986,
encoded using ASN.1 distinguished encoding rules
(DER), as specified in ITU-T X.690.";
reference
"RFC 2986: PKCS #10: Certification Request Syntax
Specification Version 1.7
ITU-T X.690:
Information technology - ASN.1 encoding rules:
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Specification of Basic Encoding Rules (BER),
Canonical Encoding Rules (CER) and Distinguished
Encoding Rules (DER).";
}
}
}
container csr-generation {
description
"Specifies details for the SZTP-client's ability to
generate a certificate signing requests.";
container supported-formats {
description
"A list of certificate request formats supported
by the SZTP-client for generating a new key.";
leaf-list format-identifier {
type identityref {
base certificate-request-format;
}
min-elements 1;
description
"A certificate request format supported by the
SZTP-client.";
}
}
}
}
container csr {
presence "Indicates that the SZTP-client has sent a CSR.";
description
"The 'csr' node enables the SZTP-client to convey
a certificate signing request, using the encoding
format selected by the SZTP-server's 'request-info'
response to the SZTP-client's previously sent
'get-bootstrapping-data' request containing the
'csr-support' node.
When present, the SZTP-server SHOULD respond with
an SZTP onboarding information message containing
a signed certificate for the conveyed CSR. The
SZTP-server MAY alternatively respond with another
HTTP error containing another 'request-info', in
which case the SZTP-client MUST invalidate the CSR
sent in this node.";
choice request-type {
mandatory true;
description
"A choice amongst certificate signing request formats.
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Additional formats MAY be augmented into this 'choice'
statement by future efforts.";
case p10 {
leaf p10 {
type ct:csr;
description
"A CertificationRequest structure, per RFC 2986.
Please see 'csr' in RFC AAAA for encoding details.";
reference
"RFC 2986: PKCS #10: Certification
Request Syntax Specification
RFC AAAA: YANG Data Types and Groupings
for Cryptography";
}
}
case cmc {
leaf cmc {
type binary;
description
"A constrained version of the 'Full PKI Request'
message defined in RFC 5272, encoded using ASN.1
distinguished encoding rules (DER), as specified
in ITU-T X.690.
For asymmetric key-based origin authentication
of a CSR based on the IDevID's private key for the
associated IDevID's public key, the PKIData contains
one reqSequence element and no controlSequence,
cmsSequence, or otherMsgSequence elements. The
reqSequence is the TaggedRequest and it is the tcr
CHOICE. The tcr is the TaggedCertificationRequest
and it a bodyPartId and the certificateRequest
elements. The certificateRequest is signed with
the IDevID's private key.
For asymmetric key-based origin authentication
based on the IDevID's private key that encapsulates
a CSR signed by the LDevID's private key, the
PKIData contains one cmsSequence element and no
controlSequence, reqSequence, or otherMsgSequence
elements. The cmsSequence is the TaggedContentInfo
and it includes a bodyPartID element and a
contentInfo. The contentInfo is a SignedData
encapsulating a PKIData with one reqSequence
element and no controlSequence, cmsSequence, or
otherMsgSequence elements. The reqSequence is
the TaggedRequest and it is the tcr CHOICE. The
tcr is the TaggedCertificationRequest and it a
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bodyPartId and the certificateRequest elements.
The certificateRequest is signed with the LDevID's
private key.
For shared secret-based origin authentication of
a CSR signed by the LDevID's private key, the
PKIData contains one cmsSequence element and no
controlSequence, reqSequence, or otherMsgSequence
elements. The cmsSequence is the TaggedContentInfo
and it includes a bodyPartID element and a
contentInfo. The contentInfo is an AuthenticatedData
encapsulating a PKIData with one reqSequence
element and no controlSequence, cmsSequence, or
otherMsgSequence elements. The reqSequence is the
TaggedRequest and it is the tcr CHOICE. The tcr
is the TaggedCertificationRequest and it a
bodyPartId and the certificateRequest elements.
The certificateRequest is signed with the LDevID's
private key.";
reference
"RFC 5272: Certificate Management over CMS (CMC)
ITU-T X.690:
Information technology - ASN.1 encoding rules:
Specification of Basic Encoding Rules (BER),
Canonical Encoding Rules (CER) and Distinguished
Encoding Rules (DER).";
}
}
case cmp {
leaf cmp {
type binary;
description
"A PKIMessage structure, as defined in RFC 4210,
encoded using ASN.1 distinguished encoding rules
(DER), as specified in ITU-T X.690.
The PKIMessage structure contains a PKCS#10
Certificate Signing Request (p10cr), as defined in
RFC 2986, encapsulated in a Nested Message Content
(nested) structure, as defined in RFC 4210.
For asymmetric key-based origin authentication of
a CSR based on the IDevID's private key for the
associated IDevID's public key, PKIMessages contains
one PKIMessage with one body element, a header
element that is an empty sequence, and no protection
or extraCerts elements. The body element contains a
p10cr CHOICE.
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For asymmetric key-based origin authentication based
on the IDevID's private key that encapsulates a CSR
signed by the LDevID's private key, PKIMessages
contains one PKIMessage with one header element,
one body element, one protection element, and one
extraCerts element. The header element contains
pvno, sender, recipient, and protectionAlg elements
and no other elements. The body element contains the
nested CHOICE. The nested element's PKIMessages
contains one PKIMessage with one body element, one
header element that is an empty sequence, and no
protection or extraCerts elements. The nested
element's body element contains a p10cr CHOICE. The
protection element contains the digital signature
generated with the IDevID's private key. The
extraCerts element contains the IDevID certificate.
For shared secret-based origin authentication of a
CSR signed by the LDevID's private key, PKIMessages
contains one PKIMessage with one header element,
one body element, one protection element, and no
extraCerts element. The header element contains
pvno, sender, recipient, and protectionAlg elements
and no other elements. The body element contains
the nested CHOICE. The nested element's PKIMessages
contains one PKIMessage with one body element, one
header element that is an empty sequence, and no
protection or extraCerts elements. The body element
contains a p10cr CHOICE. The protection element
contains the MAC value generated with the shared
secret.";
reference
"RFC 2986:
PKCS #10: Certification Request Syntax
Specification Version 1.7
RFC 4210:
Internet X.509 Public Key Infrastructure
Certificate Management Protocol (CMP)
ITU-T X.690:
Information technology - ASN.1 encoding rules:
Specification of Basic Encoding Rules (BER),
Canonical Encoding Rules (CER) and Distinguished
Encoding Rules (DER).";
}
}
}
}
}
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}
sx:structure request-info {
container key-generation {
presence
"Indicates that the SZTP-client is to generate a new
asymmetric key. If missing, then the SZTP-client
MUST reuse the key associated with its existing
identity certificate (e.g., IDevID).
This leaf MUST only appear if the SZTP-clients
'csr-support' included the 'key-generation' node.";
description
"A YANG data structure, per RFC 8791, that specifies
details for the key that the SZTP-client is to
generate.";
reference
"RFC 8791: YANG Data Structure Extensions";
container selected-algorithm {
description
"The key algorithm selected by the SZTP-server. The
algorithm MUST be one of the algorithms specified
by the 'supported-algorithms' node in the
SZTP-client's request message.";
leaf algorithm-identifier {
type binary;
mandatory true;
description
"An AlgorithmIdentifier, as defined in RFC 2986,
encoded using ASN.1 distinguished encoding rules
(DER), as specified in ITU-T X.690.";
reference
"RFC 2986: PKCS #10: Certification Request Syntax
Specification Version 1.7
ITU-T X.690:
Information technology - ASN.1 encoding rules:
Specification of Basic Encoding Rules (BER),
Canonical Encoding Rules (CER) and Distinguished
Encoding Rules (DER).";
}
}
}
container csr-generation {
description
"Specifies details for the CSR that the SZTP-client
is to generate.";
container selected-format {
description
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"The CSR format selected by the SZTP-server. The
format MUST be one of the formats specified by
the 'supported-formats' node in the SZTP-client's
request message.";
leaf format-identifier {
type identityref {
base certificate-request-format;
}
mandatory true;
description
"A certificate request format to be used by the
SZTP-client.";
}
}
}
leaf cert-req-info {
type ct:csr-info;
description
"A CertificationRequestInfo structure, as defined in
RFC 2986, and modeled via a 'typedef' statement by
RFC AAAA.
Enables the SZTP-server to provide a fully-populated
CertificationRequestInfo structure that the SZTP-client
only needs to sign in order to generate the complete
'CertificationRequest' structure to send to SZTP-server
in its next 'get-bootstrapping-data' request message.
When provided, the SZTP-client SHOULD use this
structure to generate its CSR; failure to do so MAY
result in a 400 Bad Request response containing
another 'request-info' structure.
When not provided, the SZTP-client SHOULD generate a
CSR using the same structure defined in its existing
identity certificate (e.g., IDevID).
It is an error if the 'AlgorithmIdentifier' field
contained inside the 'SubjectPublicKeyInfo' field
does not match the algorithm identified by the
'selected-algorithm' node.";
reference
"RFC 2986:
PKCS #10: Certification Request Syntax Specification
RFC AAAA:
YANG Data Types and Groupings for Cryptography";
}
}
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}
<CODE ENDS>
3. Security Considerations
This document builds on top of the solution presented in [RFC8572]
and therefore all the Security Considerations discussed in RFC 8572
apply here as well.
3.1. SZTP-Client Considerations
3.1.1. Ensuring the Integrity of Asymmetric Private Keys
The private key the SZTP-client uses for the dynamically-generated
identity certificate MUST be protected from inadvertent disclosure in
order to prevent identity fraud.
The security of this private key is essential in order to ensure the
associated identity certificate can be used as a root of trust.
It is RECOMMENDED that devices are manufactured with an HSM (hardware
security module), such as a TPM (trusted platform module), to
generate and forever contain the private key within the security
perimeter of the HSM. In such cases, the private key, and its
associated certificates, MAY have long validity periods.
In cases where the device does not possess an HSM, or otherwise is
unable to use an HSM for the private key, it is RECOMMENDED to
regenerate the private key (and associated identity certificates)
periodically. Details for how to generate a new private key and
associate a new identity certificate are outside the scope of this
document.
3.1.2. Reuse of a Manufacturer-generated Private Key
It is RECOMMENDED that a new private key is generated for each CSR
described in this document.
This private key SHOULD be protected as well as the built-in private
key associated with the device's initial secure device identity
certificate (e.g., the IDevID, from [Std-802.1AR-2018]).
In cases where it is not possible to generate a new private key that
is protected as well as the built-in private key, it is RECOMMENDED
to reuse the built-in private key rather than generate a new private
key that is not as well protected.
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3.1.3. Replay Attack Protection
This RFC enables an SZTP-client to announce an ability to generate a
new key to use for its CSR.
When the SZTP-server responds with a request for the device to
generate a new key, it is essential that the device actually
generates a new key.
Generating a new key each time enables the random bytes used to
create the key to also serve the dual-purpose of acting like a
"nonce" used in other mechanisms to detect replay attacks.
When a fresh public/private key pair is generated for the request,
confirmation to the SZTP-client that the response has not been
replayed is enabled by the SZTP-client's fresh public key appearing
in the signed certificate provided by the SZTP-server.
When a public/private key pair associated with the manufacturer-
generated identity certificate (e.g., IDevID) is used for the
request, there may not be confirmation to the SZTP-client that the
response has not been replayed; however, the worst case result is a
lost certificate that is associated to the private key known only to
the SZTP-client.
3.1.4. Connecting to an Untrusted Bootstrap Server
[RFC8572] allows SZTP-clients to connect to untrusted SZTP-servers,
by blindly authenticating the SZTP-server's TLS end-entity
certificate.
As is discussed in Section 9.5 of [RFC8572], in such cases the SZTP-
client MUST assert that the bootstrapping data returned is signed, if
the SZTP-client is to trust it.
However, the HTTP error message used in this document cannot be
signed data, as described in RFC 8572.
Therefore, the solution presented in this document cannot be used
when the SZTP-client connects to an untrusted SZTP-server.
Consistent with the recommendation presented in Section 9.6 of
[RFC8572], SZTP-clients SHOULD NOT pass the "csr-support" input
parameter to an untrusted SZTP-server. SZTP-clients SHOULD pass
instead the "signed-data-preferred" input parameter, as discussed in
Appendix B of [RFC8572].
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3.1.5. Selecting the Best Origin Authentication Mechanism
When generating a new key, it is important that the client be able to
provide additional proof to the CA that it was the entity that
generated the key.
All the certificate request formats defined in this document (e.g.,
CMC, CMP, etc.), not including a raw PKCS#10, support origin
authentication.
These formats support origin authentication using both PKI and shared
secret.
Typically, only one possible origin authentication mechanism can
possibly be used but, in the case that the SZTP-client authenticates
itself using both TLS-level (e.g., IDevID) and HTTP-level credentials
(e.g., Basic), as is allowed by Section 5.3 of [RFC8572], then the
SZTP-client may need to choose between the two options.
In the case that the SZTP-client must choose between the asymmetric
key option versus a shared secret for origin authentication, it is
RECOMMENDED that the SZTP-client choose using the asymmetric key
option.
3.1.6. Clearing the Private Key and Associated Certificate
Unlike a manufacturer-generated identity certificate (e.g., IDevID),
the deployment-generated identity certificate (e.g., LDevID) and the
associated private key (assuming a new private key was generated for
the purpose), are considered user data and SHOULD be cleared whenever
the device is reset to its factory default state, such as by the
"factory-reset" RPC defined in [I-D.ietf-netmod-factory-default].
3.2. SZTP-Server Considerations
3.2.1. Conveying Proof of Possession to a CA
When the bootstrapping device's manufacturer-generated private key
(e.g., the IDevID key) is reused, a CA may validate that the CSR was
signed by that key.
Both the CMP and CMC formats entail the bootstrapping device signing
the request once with its (e.g., LDevID) key and then again with its
(e.g., IDevID) key, which enables a downstream CA to be assured that
the device possesses the public key being signed.
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3.2.2. Supporting SZTP-Clients that don't trust the SZTP-Server
[RFC8572] allows SZTP-clients to connect to untrusted SZTP-servers,
by blindly authenticating the SZTP-server's TLS end-entity
certificate.
As is recommended in Section 3.1.4 in this document, in such cases,
SZTP-clients SHOULD pass the "signed-data-preferred" input parameter.
The reciprocal of this statement is that SZTP-servers, wanting to
support SZTP-clients that don't trust them, SHOULD support the
"signed-data-preferred" input parameter, as discussed in Appendix B
of [RFC8572].
3.2.3. YANG Module Considerations
The recommended format for documenting the Security Considerations
for YANG modules is described in Section 3.7 of [RFC8407]. However,
the module defined in this document only augments two input
parameters into the "get-bootstrapping-data" RPC in [RFC8572], and
therefore only needs to point to the relevant Security Considerations
sections in that RFC.
* Security considerations for the "get-bootstrapping-data" RPC are
described in Section 9.16 of [RFC8572].
* Security considerations for the "input" parameters passed inside
the "get-bootstrapping-data" RPC are described in Section 9.6 of
[RFC8572].
4. IANA Considerations
4.1. The "IETF XML" Registry
This document registers one URI in the "ns" subregistry of the IETF
XML Registry [RFC3688] maintained at
https://www.iana.org/assignments/xml-registry/xml-registry.xhtml#ns.
Following the format in [RFC3688], the following registration is
requested:
URI: urn:ietf:params:xml:ns:yang:ietf-sztp-csr
Registrant Contact: The NETCONF WG of the IETF.
XML: N/A, the requested URI is an XML namespace.
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4.2. The "YANG Module Names" Registry
This document registers one YANG module in the YANG Module Names
registry [RFC6020] maintained at https://www.iana.org/assignments/
yang-parameters/yang-parameters.xhtml. Following the format defined
in [RFC6020], the below registration is requested:
name: ietf-sztp-csr
namespace: urn:ietf:params:xml:ns:yang:ietf-sztp-csr
prefix: sztp-csr
reference: RFC XXXX
5. References
5.1. Normative References
[I-D.ietf-netconf-crypto-types]
Watsen, K., "YANG Data Types and Groupings for
Cryptography", Work in Progress, Internet-Draft, draft-
ietf-netconf-crypto-types-19, 10 February 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
crypto-types-19>.
[ITU.X690.2015]
International Telecommunication Union, "Information
Technology - ASN.1 encoding rules: Specification of Basic
Encoding Rules (BER), Canonical Encoding Rules (CER) and
Distinguished Encoding Rules (DER)", ITU-T Recommendation
X.690, ISO/IEC 8825-1, August 2015,
<https://www.itu.int/rec/T-REC-X.690/>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2986] Nystrom, M. and B. Kaliski, "PKCS #10: Certification
Request Syntax Specification Version 1.7", RFC 2986,
DOI 10.17487/RFC2986, November 2000,
<https://www.rfc-editor.org/info/rfc2986>.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC3688, January 2004,
<https://www.rfc-editor.org/info/rfc3688>.
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[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC6020, October 2010,
<https://www.rfc-editor.org/info/rfc6020>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/info/rfc7950>.
[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
<https://www.rfc-editor.org/info/rfc8040>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8572] Watsen, K., Farrer, I., and M. Abrahamsson, "Secure Zero
Touch Provisioning (SZTP)", RFC 8572,
DOI 10.17487/RFC8572, April 2019,
<https://www.rfc-editor.org/info/rfc8572>.
5.2. Informative References
[I-D.ietf-netconf-keystore]
Watsen, K., "A YANG Data Model for a Keystore", Work in
Progress, Internet-Draft, draft-ietf-netconf-keystore-21,
10 February 2021, <https://datatracker.ietf.org/doc/html/
draft-ietf-netconf-keystore-21>.
[I-D.ietf-netconf-trust-anchors]
Watsen, K., "A YANG Data Model for a Truststore", Work in
Progress, Internet-Draft, draft-ietf-netconf-trust-
anchors-14, 10 February 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-netconf-
trust-anchors-14>.
[I-D.ietf-netmod-factory-default]
Wu, Q., Lengyel, B., and Y. Niu, "A YANG Data Model for
Factory Default Settings", Work in Progress, Internet-
Draft, draft-ietf-netmod-factory-default-15, 25 April
2020, <https://datatracker.ietf.org/doc/html/draft-ietf-
netmod-factory-default-15>.
[RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
<https://www.rfc-editor.org/info/rfc8340>.
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[RFC8407] Bierman, A., "Guidelines for Authors and Reviewers of
Documents Containing YANG Data Models", BCP 216, RFC 8407,
DOI 10.17487/RFC8407, October 2018,
<https://www.rfc-editor.org/info/rfc8407>.
[Std-802.1AR-2018]
Group, W. -. H. L. L. P. W., "IEEE Standard for Local and
metropolitan area networks - Secure Device Identity", 14
June 2018, <http://standards.ieee.org/findstds/
standard/802.1AR-2018.html>.
Authors' Addresses
Kent Watsen
Watsen Networks
Email: kent+ietf@watsen.net
Russ Housley
Vigil Security, LLC
Email: housley@vigilsec.com
Sean Turner
sn3rd
Email: sean@sn3rd.com
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